Transport of printable substrates formed by suction belts in known from the prior art, the function of which is to hold and keep a substrate against said belts as they move. This type of solution, well known to those skilled in the art, has a few disadvantages however. In particular, this type of device, causing movements of air and pressure gradients, can cause deformation of substrates if the latter are large in size. The precision of the printing will therefore be affected. On the other hand, the use of these suction belts with some wide used printing technologies, especially inkjet printing, can cause accidental aspiration of ink present in the printing heads and cause the deactivation of the printing heads. In the best of cases this genre of incident needs reactivating of the heads, and in the worst of cases replacement of the deactivated heads, the latter now unusable if connected to the ink tank.
To rectify these problems, especially to allow displacement of substrates precisely, there are in the prior art techniques using cylinders comprising a plurality of clamps gripping the substrates by the front edge relative to the direction of displacement of the substrate. Adapted to printing machines of inkjet type, this type of solution has several disadvantages however. Indeed, this system needs all the heads inkjet to be arranged orbitally around a large-sized cylinder. Also, this type of system poses the problem of the difficulty in adjusting the position of the printing heads. In fact, for quality printing, ink ejected from the printing heads must form a jet whereof the direction is perpendicular to the surface of the substrate. It is understood in this case that the use of a cylinder to transport and hold the substrate, whereof the surface by definition is not flat, means intricate adjusting of the position of the printing heads. For this same reason, it is difficult to use substrates of variable thickness, as the change of substrate means adjusting all the printing heads. On the other hand, the printing pitch, that is, the position of the clamps on the cylinder, is fixed, meaning that the printing rate remains the same irrespective of the size of the substrate.
Also known from the prior art are substrate transport systems using chains or conveyors on which clamps are arranged to grip the substrates and transport them on a transport path whereof a portion is flat, resolving the problem of arrangement of the printing heads. However, this type of solution always has the problem of fixed printing pitch, which imposes a fixed rate and in this case poses the extra problem of not being able to use substrates of different sizes without stopping printing and proceeding with intricate adjusting of the position of the clamps.